ZnO based semiconductor devices and methods of manufacturing the same

ABSTRACT

A semiconductor device may include a composite represented by Formula 1 below as an active layer.
 
x(Ga 2 O 3 )·y(In 2 O 3 )·z(ZnO)  Formula 1
 
wherein, about 0.75≦x/z≦ about 3.15, and about 0.55≦y/z≦ about 1.70.
 
     Switching characteristics of displays and driving characteristics of driving transistors may be improved by adjusting the amounts of a gallium (Ga) oxide and an indium (In) oxide mixed with a zinc (Zn) oxide and improving optical sensitivity.

PRIORITY STATEMENT

This non-provisional application claims priority under 35 U.S.C. §119 toKorean Patent Application Nos. 10-2006-0034675, filed on Apr. 17, 2006,10-2006-0043943, filed on May 16, 2006, and 10-2007-0029380, filed onMar. 26, 2007 in the Korean Intellectual Property Office (KIPO), theentire contents of which are incorporated herein by reference.

BACKGROUND

1. Field

Example embodiments relate to a semiconductor device and methods ofmanufacturing the same. Other example embodiments relate to a ZnO basedthin film transistor including an active layer using a compositesemiconductor material in which a zinc (Zn) oxide is doped with gallium(Ga) and indium (In) and methods of manufacturing the same.

2. Description of the Related Art

Research on organic light-emitting diodes (OLED) having a relativelylarge area has been actively conducted. As a driving transistor forOLEDs, a transistor that stably operates with constant currentcharacteristics and has improved durability needs to be developed.Amorphous silicon TFTs may be manufactured using a low temperatureprocess, but such TFTs may have relatively low mobility and may notsatisfy constant current bias conditions. On the other hand,polycrystalline silicon TFTs may have increased mobility and may satisfyconstant current test conditions, but may not have uniformcharacteristics. Thus, polycrystalline silicon TFTs may not haverelatively large areas and may require high temperature processes.

ZnO materials may have conductivity, semiconductivity, and resistanceaccording to their oxygen content. A transistor including a ZnO basedsemiconductor material as an active layer has been reported. In order toapply the transistor including a ZnO based semiconductor material as anactive layer to display devices including OLEDs and LCDs, stable drivingcharacteristics, which present constant characteristics in an on or offstate, may be required in addition to constant current characteristics.

SUMMARY

Example embodiments provide an amorphous ZnO based thin film transistorhaving constant driving characteristics in an on or off state due toimproved optical sensitivity, and methods of manufacturing the same.

According to example embodiments, a semiconductor device may include asubstrate, an active layer including a composite represented by Formula1 below, on the substrate, source and drain electrodes electricallyconnected to the active layer, a gate electrode on the active layer, anda gate insulating layer between the gate electrode and the active layer:x(Ga₂O₃)·y(In₂O₃)·z(ZnO)  Formula 1wherein, about 0.75≦x/z≦about 3.15, and about 0.55≦y/z≦about 1.70.

According to example embodiments, x, y, and z may be about0.85≦x/z≦about 3.05, and about 0.65≦y/z≦about 1.70 in Formula 1.According to example embodiments, x, y, and z may be about1.15≦x/z≦about 2.05, and about 1.15≦y/z≦about 1.70 in Formula 1.According to example embodiments, x, y, and z may be about1.25≦x/z≦about 1.95, and about 1.25≦y/z≦about 1.70 in Formula 1.According to example embodiments, x, y, and z may be about1.25≦x/z≦about 1.45, and about 1.45≦y/z≦about 1.65 in Formula 1.

According to example embodiments, a method of manufacturing asemiconductor device may include forming an active layer including acomposite represented by Formula 1 below, source and drain electrodes, agate insulating layer and a gate electrode on a substrate,x(Ga₂O₃)·y(In₂O₃)·z(ZnO)  Formula 1wherein, about 0.75≦x/z≦about 3.15, and about 0.55≦y/z≦about 1.70.

According to example embodiments, the active layer may be formed on thesubstrate, the source and drain electrodes may be formed to beelectrically connected to the active layer, the gate insulating layermay be formed on the active layer, and the gate electrode may be formedon the active layer. On the other hand, the gate electrode may be formedon the substrate, the gate insulating layer may be formed on the gateelectrode, the active layer may be formed on the gate insulating layer,and the source and drain electrodes may be formed to be electricallyconnected to the active layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Example embodiments will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings. FIGS. 1-5 represent non-limiting, example embodiments asdescribed herein.

FIG. 1 is a schematic cross-sectional view of a semiconductor deviceaccording to example embodiments;

FIG. 2 is a schematic cross-sectional view of a semiconductor deviceaccording to example embodiments;

FIGS. 3A-3G are cross-sectional views illustrating a method ofmanufacturing the example embodiment shown in FIG. 1;

FIGS. 4A-4E are cross-sectional views illustrating a method ofmanufacturing another example embodiment shown in FIG. 2;

FIG. 5 is a graph illustrating results of an inductively coupled plasma(ICP) analysis of ZnO based TFTs;

FIGS. 6-10 are graphs illustrating results of an optical sensitivityanalysis of ZnO based TFTs, and variations in a gate voltage (Vg) and adrain current (Id);

FIG. 11 is a graph illustrating results of a constant current test of aZnO based TFT; and

FIGS. 12 and 13 are graphs illustrating variations in a gate voltage(Vg) and a drain current (Id) of the ZnO based TFT before and after theconstant current test.

It should be noted that these Figures are intended to illustrate thegeneral characteristics of methods, structure and/or materials utilizedin certain example embodiments and to supplement the written descriptionprovided below. These drawings are not, however, to scale and may notprecisely reflect the precise structural or performance characteristicsof any given embodiment, and should not be interpreted as defining orlimiting the range of values or properties encompassed by exampleembodiments. For example, the relative thicknesses and positioning ofmolecules, layers, regions and/or structural elements may be reduced orexaggerated for clarity. The use of similar or identical referencenumbers in the various drawings is intended to indicate the presence ofa similar or identical element or feature.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS

Hereinafter, example embodiments will now be described more fully withreference to the accompanying drawings, in which example embodiments areshown. Example embodiments may, however, be embodied in many differentforms and should not be construed as being limited to the embodimentsset forth herein; rather, these embodiments are provided so that thisdisclosure will be thorough and complete, and will fully convey theconcept of example embodiments to those skilled in the art.

It will be understood that when an element or layer is referred to asbeing “on”, “connected to” or “coupled to” another element or layer, itcan be directly on, connected or coupled to the other element or layeror intervening elements or layers may be present. In contrast, when anelement is referred to as being “directly on,” “directly connected to”or “directly coupled to” another element or layer, there are nointervening elements or layers present. Like numbers refer to likeelements throughout. As used herein, the term “and/or” includes any andall combinations of one or more of the associated listed items.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of example embodiments.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of exampleembodiments. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

Example embodiments are described herein with reference tocross-sectional illustrations that are schematic illustrations ofidealized embodiments (and intermediate structures) of exampleembodiments. As such, variations from the shapes of the illustrations asa result, for example, of manufacturing techniques and/or tolerances,are to be expected. Thus, example embodiments should not be construed aslimited to the particular shapes of regions illustrated herein but areto include deviations in shapes that result, for example, frommanufacturing. For example, an implanted region illustrated as arectangle will, typically, have rounded or curved features and/or agradient of implant concentration at its edges rather than a binarychange from implanted to non-implanted region. Likewise, a buried regionformed by implantation may result in some implantation in the regionbetween the buried region and the surface through which the implantationtakes place. Thus, the regions illustrated in the figures are schematicin nature and their shapes are not intended to illustrate the actualshape of a region of a device and are not intended to limit the scope ofexample embodiments.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which example embodiments belong. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

FIG. 1 is a schematic cross-sectional view of a semiconductor deviceaccording to example embodiments. Referring to FIG. 1, a patternedactive layer 11 including an amorphous ZnO based composite semiconductormay be formed on a substrate 10, and source and drain electrodes 12 sand 12 d may be formed on ends of the patterned active layer asillustrated in FIG. 1. The source and drain electrodes 12 s and 12 d mayoverlap with the ends of the patterned active layer 11 in apredetermined or given width, and may be insulated from a gate electrode14.

The active layer 11 may include an amorphous ZnO based compositematerial represented by Formula 1 below.x(Ga₂O₃)·y(In₂O₃)·z(ZnO)  Formula 1wherein, about 0.75≦x/z≦about 3.15, and about 0.55≦y/z≦about 1.70.

In the amorphous ZnO based composite semiconductor, when the amount ofGa is too low, the Ioff current may increase when exposed to light dueto its light-sensitive characteristics. On the other hand, when theamount of Ga is too high, an Ion/Ioff ratio may decrease, resulting inthe deterioration of TFT characteristics. When the amount of Ion currentis too low, mobility of a carrier may decrease. On the other hand, whenthe amount of In current is too high, threshold voltage may vary due toits light-sensitive characteristics.

In the above formula, x, y and z may be about 0.75≦x/z≦about 3.15, andabout 0.55≦y/z≦about 1.70, for example, about 0.85≦x/z≦about 3.05, andabout 0.65≦y/z≦about 1.70, or about 1.15≦x/z≦about 2.05, and1.15≦y/z≦1.70, or about 1.25≦x/z≦about 1.95, and about 1.25≦y/z≦about1.70, or about 1.25≦x/z≦about 1.45, and about 1.45≦y/z≦about 1.65.

The amorphous ZnO based composite semiconductor material represented byFormula 1 may be applied to a low temperature deposition, e.g., aplastic substrate and a soda lime glass. The amorphous property mayprovide uniformity for a display having relatively large areas. Theamorphous ZnO based composite semiconductor may be formed using acomposite target of a gallium (Ga) oxide, an indium (In) oxide, and azinc (Zn) oxide by a conventional sputtering method, and also formedusing chemical vapor deposition (CVD) and/or an atomic layer deposition(ALD).

The source and drain electrodes 12 s and 12 d may be formed of aconductive metal oxide or a metal. Examples of the conductive metaloxide may include commonly available tin-doped indium oxide (ITO),indium zinc oxide (IZO), and/or aluminum-doped zinc oxide (ZAO), andexamples of the metal may include titanium (Ti), platinum (Pt), chromium(Cr), tungsten (W), aluminum (Al), nickel (Ni), copper (Cu), molybdenum(Mo), tantalum (Ta), and/or an alloy thereof. When a metal layer is usedas the source and drain electrodes, a plurality of metal layers may beformed. When the metal layer is used, an n⁺ layer may be formed betweenthe metal layer and the active layer to improve contact characteristics,and the n⁺ layer may be formed using a conductive metal oxide or anoxygen vacant Ga oxide-In oxide-Zn oxide composite. The substrate may bea silicon substrate, a glass substrate and/or a plastic substrate.

A gate insulating layer 13 may be formed on the active layer 11 and thesource/drain electrodes 12 s and 12 d. A commonly available gateinsulating material may be used to form the gate insulating layer 13,for example, a high dielectric oxide (e.g., a silicon nitride, a siliconoxide, a hafnium oxide and/or an aluminum oxide), may be used.

A gate electrode 14 may be formed on the gate insulating layer 13 andmay correspond to the active layer 11. The gate electrode 14 may beformed using the same metal used for a source/drain electrode layer 120or other metals. For example, a metal of Ti, Pt, Cr, W, Al, Ni, Cu, Mo,or Ta, or an alloy thereof may be used. When the metal layer is used asthe gate electrode, a plurality of metal layers may be formed. A metaloxide may also be used.

The semiconductor device may have the structure illustrated in FIG. 2 bydisposing the gate electrode in a different way from the structureillustrated in FIG. 1. Referring to FIG. 2, a gate electrode 21 may beformed on a substrate 20, and a gate insulating layer 22 may be formedon the gate electrode 21. A patterned active layer 23 including anamorphous ZnO based composite semiconductor may be formed on the gateinsulating layer 22. Source and drain electrodes 24 s and 24 d may beformed on ends of the patterned active layer 23.

Another example of a semiconductor device according to exampleembodiments may also have a structure in which source/drain electrodesmay be formed on a gate insulating layer and then an active layer may beformed on the source/drain electrodes, besides the stack structureillustrated in FIGS. 1 and 2.

A method of manufacturing a semiconductor device according to exampleembodiments will now be described in detail. FIGS. 3A-3G arecross-sectional views illustrating a method of manufacturing thesemiconductor device shown in FIG. 1. As shown in FIG. 3A, asemiconductor material layer 11′ may be formed on the substrate 10 toform the active layer 11 using a RF magnetron sputtering method, a DCmagnetron sputtering method, a chemical vapor deposition (CVD) methodand/or an atomic layer deposition (ALD) method.

As shown in FIG. 3B, the semiconductor material layer 11′ may bepatterned using a photolithographic method to obtain the active layer11. As shown in FIG. 3C, a source/drain material layer 12 may be formedon the entire surface of the active layer 11 using a RF magnetronsputtering method, a CVD method, a vacuum evaporation method, an e-beamevaporation method and/or an ALD method.

As shown in FIG. 3D, the source/drain material layer 12 may be patternedto form the source and drain electrodes 12 s and 12 d contacting theends of the active layer 11. As shown in FIG. 3E, a material that isused to form the gate insulating layer 13 may be deposited using aconventional method, e.g., chemical vapor deposition (CVD) method and/ora plasma enhanced chemical vapor deposition (PECVD) method, to form thegate insulating layer 13 covering the source and drain electrodes 12 sand 12 d on the entire surface of the resultant stack structure. Asshown in FIG. 3F, a material for forming a gate electrode may bedeposited and patterned to form the gate electrode 14 facing the activelayer 11.

As shown in FIG. 3G, the stack structure including the active layer 11and the source and drain electrodes 12 s and 12 d contacting the ends ofthe active layer 11 may be annealed at a temperature of about 400° C. orless. Annealing may be performed using a general furnace, a rapidthermal annealing (RTA), a laser, or a hot plate in a nitrogenatmosphere. Annealing may stabilize a contact between the active layer11 and the source/drain electrodes 12 s and 12 d.

FIGS. 4A-4E are cross-sectional views illustrating a method ofmanufacturing the semiconductor device shown in FIG. 2. As shown in FIG.4A, a material for forming the gate electrode 21 may be deposited on thesubstrate 20 and patterned to form the gate electrode 21. As shown inFIG. 4B, the gate insulating layer 22 may be formed on the gateelectrode 21. The gate insulating layer 22 may be formed using CVD orPECVD. As shown in FIG. 4C, a semiconductor film formed using a targetthat for forming an amorphous ZnO based composite semiconductorrepresented by Formula 1 above may be patterned to obtain the activelayer 23 using a photolithographic method. As shown in FIG. 4D, asource/drain electrode material may be deposited and patterned to obtainthe source and drain electrodes 24 s and 24 d.

As shown in FIG. 4E, the stack structure including the active layer 23and the source and drain electrodes 24 s and 24 d contacting the ends ofthe active layer 23 may be annealed. Annealing may be performed at atemperature of about 450° C. or less, for example, about 200° C. toabout 350° C., in an inert gas atmosphere, e.g., a nitrogen atmosphere.The annealing may be performed using a general furnace, a RTA, a laser,or a hot plate. Annealing may stabilize a contact between the activelayer 23 and the source/drain electrodes 24 s and 24 d.

A semiconductor film may be formed using a composite oxide target ofgallium (Ga), indium (In), and zinc (Zn) in an atomic ratio of about1:1:1, about 2:2:1, about 3:2:1 and about 4:2:1 by using molybdenum (Mo)as a gate electrode material after forming a silicon nitride layer usinga gate insulating material. The semiconductor film may be patterned toform an active layer. IZO may be deposited and patterned to formsource/drain electrodes, the resultant may be annealed in a nitrogenatmosphere and a passivation layer may be formed of a silicon oxide.

An inductively coupled plasma (ICP) analysis on the semiconductor filmformed according to the processes described above may be performed tomeasure the ratio of gallium (Ga), indium (In) and zinc (Zn), and theresults are shown in Table 1 below and FIG. 5. Variations in a gatevoltage (Vg) and a drain current (Id), when both light is on and off,are measured, and the results are shown in FIGS. 6-10.

TABLE 1 Ga, In, Zn atomic ratio in 1:1:1 2:2:1 2:2:1 3:2:1 4:2:1 thetarget Ga:In:Zn atom ratio in 1.7:1.3:1.0 2.5:2.8:1.0 2.7:3.1:1.03.9:2.5:1.0 6.1:3.2:1.0 active layer (ICP analysis) x/z 0.85 1.25 1.351.95 3.05 y/z 0.65 1.4 1.55 1.25 1.60 optical sensitivity FIG. 6 FIG. 7FIG. 8 FIG. 9 FIG. 10 analysis results ※ error range of ±0.2 in ICPanalysis

A constant current test was performed using a TFT having a Ga:In:Znratio of about 2.7:3.1:1.0, and the results are shown in FIG. 11. Theconstant current test may be performed at a temperature of about 45° C.for about 100 hours and a current applied to the source-drain electrodesmay be about 3 μA. As illustrated in FIG. 11, a voltage variation (DeltaV) between the source and drain electrodes remained at about 0.3 V orless. In addition, variations in a gate voltage (Vg) and a drain current(Id) before and after a constant current test were measured, and theresults are illustrated in FIGS. 12 and 13.

FIG. 12 is a graph illustrating results measured before a constantcurrent test. An on-current may be about 10⁻⁴ A, and an off-current maybe about 10⁻¹² A, and thus the ratio of the on-current to the offcurrent may be about 10⁸. Mobility on the active layer may be about 40cm²/Vs, and a gate swing voltage may be about 0.385 V/dec. FIG. 13 is agraph illustrating results measured after a constant current test. Uponcomparing FIGS. 12 and 13, the constant current test results may notdiffer greatly from each other. In other words, the ZnO based TFT maymaintain its original electrical characteristics even after a constantcurrent test in which about 3 μA may be applied for 100 hours.

According to example embodiments, an electrically stable TFT may beobtained by using an active layer including an amorphous ZnO basedcomposite semiconductor due to improved optical sensitivity. Theamorphous property of the ZnO based composite semiconductor may provideimproved uniformity, and thus may be applied to display devices havingrelatively large areas.

Various electronic devices and apparatuses using the ZnO based TFTaccording to example embodiments may be manufactured by those ofordinary skill in the art according to example embodiments. Whileexample embodiments have been particularly shown and described withreference to example embodiments thereof, it will be understood by thoseof ordinary skill in the art that various changes in form and detailsmay be made therein without departing from the spirit and scope of thefollowing claims.

1. A semiconductor device comprising: a substrate; an active layerincluding a composite represented by Formula 1 below, on the substrate;source and drain electrodes electrically connected to the active layer;a gate electrode on the active layer; and a gate insulating layerbetween the gate electrode and the active layer:x(Ga₂O₃)·y(In₂O₃)·z(ZnO)  Formula 1 wherein x, y, and z are about1.25≦x/z≦ about 1.45, and about 1.45≦y/z≦ about 1.65 in Formula 1, andwherein, when a drain current is 1E⁻¹⁰A, the difference of V(light on)and V(light off) is equal to or less than 5 V.
 2. The semiconductordevice of claim 1, wherein the source and drain electrodes are formed ofa metal oxide selected from the group consisting of tin-doped indiumoxide (ITO), indium zinc oxide (IZO), and aluminum-doped zinc oxide(ZAO).
 3. The semiconductor device of claim 1, wherein the source anddrain electrodes include a metal selected from the group consisting oftitanium (Ti), platinum (Pt), chromium (Cr), tungsten (W), aluminum(Al), nickel (Ni), copper (Cu), molybdenum (Mo), tantalum (Ta) and analloy thereof.
 4. The semiconductor device of claim 3, wherein thesource and drain electrodes are formed of a plurality of metal layers.5. The semiconductor device of claim 3, wherein an n+ layer is formedbetween the source or drain electrode and the active layer.
 6. Thesemiconductor device of claim 1, wherein the gate insulating layerincludes a nitride, an oxide, or a high dielectric oxide.
 7. Thesemiconductor device of claim 1, wherein the gate electrode includes ametal selected from the group consisting of titanium (Ti), platinum(Pt), chromium (Cr), tungsten (W), aluminum (Al), nickel (Ni), copper(Cu), molybdenum (Mo), tantalum (Ta) and an alloy thereof.
 8. Thesemiconductor device of claim 1, wherein the substrate is a glasssubstrate or a plastic substrate.
 9. The semiconductor of claim 1,wherein the active layer is amorphous.
 10. A method of manufacturing asemiconductor device, the method comprising: forming an active layerincluding a composite represented by Formula 1 below, source and drainelectrodes, a gate insulating layer and a gate electrode on a substrate,x(Ga₂O₃)·y(In₂O₃)·z(ZnO)  Formula 1 wherein x, y, and z are about1.25≦x/z≦ about 1.45 and about 1.45≦y/z≦ about 1.65 in Formula 1, andwherein, when a drain current is 1E⁻¹⁰A, the difference of V(light on)and V(light off) is equal to or less than 5 V.
 11. The method of claim10, wherein the active layer is formed on the substrate, the source anddrain electrodes are formed to be electrically connected to the activelayer, the gate insulating layer is formed on the active layer, and thegate electrode is formed on the active layer.
 12. The method of claim10, wherein the gate electrode is formed on the substrate, the gateinsulating layer is formed on the gate electrode, the active layer isformed on the gate insulating layer, and the source and drain electrodesare formed to be electrically connected to the active layer.
 13. Themethod of claim 10, wherein the source and drain electrodes are formedof a metal oxide.
 14. The method of claim 10, further comprising:forming an n+ layer between the active layer and the source and drainelectrodes. .
 15. The method of claim 10, further comprising: annealingthe active layer and the source and drain electrodes, after forming theactive layer and the source and drain electrodes.
 16. The method ofclaim 15, wherein annealing is performed at a temperature of about 400°or less in a nitrogen atmosphere.
 17. The method of claim 10, whereinthe active layer is amorphous.